Modulating Intracellular Dynamics for Optimized Intracellular Release and Transcytosis Equilibrium

Active transcytosis-mediated nanomedicine transport presents considerable potential in overcoming diverse delivery barriers, thereby facilitating tumor accumulation and penetration. Nevertheless, the persistent challenge lies in achieving a nuanced equilibrium between intracellular interception for drug release and transcytosis for tumor penetration. In this study, a comprehensive exploration is conducted involving a series of polyglutamine-paclitaxel conjugates featuring distinct hydrophilic/hydrophobic ratios (HHR) and tertiary amine-oxide proportions (TP) (OPGA-PTX). The screening process, meticulously focused on delineating their subcellular distribution, transcytosis capability, and tumor penetration, unveils a particularly promising candidate denoted as OPPX, characterized by an HHR of 10:1 and a TP of 100%. OPPX, distinguished by its rapid cellular internalization through multiple endocytic pathways, selectively engages in trafficking to the Golgi apparatus for transcytosis to facilitate accumulation within and penetration throughout tumor tissues and simultaneously sorted to lysosomes for cathepsin B-activated drug release. This study not only identifies OPPX as an exemplary nanomedicine but also underscores the feasibility of modulating subcellular distribution to optimize the active transport capabilities and intracellular release mechanisms of nanomedicines, providing an alternative approach to designing efficient anticancer nanomedicines.

Calcium signaling facilitates chilling- and GA- induced dormancy release in tree peony

Calcium plays a crucial role in plant growth and development, yet little is known about its function in endodormancy regulation. Tree peony (Paeonia suffruticosa), characterized by compound buds and large flowers, is well-known for its ornamental and medicinal value. To break bud dormancy release is a prerequisite of flowering and forcing culture, particularly during the Spring Festival. In this study, the Ca2+ chelator EGTA and Ca2+ channel blocker LaCl3 were applied, resulting in a significant delay in budburst during both chilling- and gibberellin (GA)- induced dormancy release in a dosage-dependent manner. As expected, the retardation of bud break was recovered by the supplementation of 30 mM CaCl2, indicating a facilitating role of calcium in dormancy release. Accordingly, several calcium-sensor-encoding genes including Calmodulin (CaM) and Ca2+-dependent protein kinases (CDPKs) were significantly up-regulated by prolonged chilling and exogenous GAs. Ultrastructure observations revealed a decline in starch grains and the reopening of transport corridors following prolonged chilling. Calcium deposits were abundant in the cell walls and intercellular spaces at the early dormant stage but were enriched in the cytosol and nucleus before dormancy release. Additionally, several genes associated with dormancy release, including EBB1, EBB3, SVP, GA20ox, RGL1, BG6, and BG9, were differentially expressed after calcium blocking and recovery treatments, indicating that calcium might partially modulate dormancy release through GA and ABA pathways. Our findings provide novel insights into the mechanism of dormancy release and offer potential benefits for improving and perfecting forcing culture technology in tree peonies.

Comparative study of the steady-state subcellular distribution of lysosome-associated membrane glycoprotein-2 (LAMP-2) isoforms with GYXXΦ-type tyrosine-based motifs that interact differently with four adaptor protein (AP) complexes

Lysosome-associated membrane protein-1 and -2 (LAMP-1 and LAMP-2, respectively) are type I transmembrane proteins. LAMP-2 comprises three splice isoforms (LAMP-2A, -B and-C) with different cytoplasmic tails (CTs). These three CTs possess different tyrosine-based motifs (GYXXΦ, where Φ is a bulky hydrophobic amino acid) at their C-termini. Interactions between tyrosine-based motifs and μ-subunits of four tetrameric adaptor protein (AP) complexes are necessary for their vesicular transport to lysosomes. Little is known about how the interaction strengths of these tyrosine motifs with μ-subunits affect the localization of isoforms to lysosomes. The interactions were first investigated using a yeast two-hybrid system to address this question. LAMP-2A-CT interacted with all four μ-subunits (μ1, μ2, μ3A and μ4 of AP-1, AP-2, AP-3 and AP-4, respectively). The interaction with μ3A was more robust than that with other μ-subunits. LAMP-2B-CT interacted exclusively and moderately with μ3A. LAMP-2C-CT did not detectably interact with any of the four μ-subunits. Immunofluorescence microscopy showed that all isoforms were localized in late endosomes and lysosomes. LAMP-2C was present in the plasma membrane and early endosomes; however, LAMP-2A and -2B were barely detectable in these organelles. In cell fractionation, LAMP-2A was the most abundant in the dense lysosomes, whereas LAMP-2C was significantly present in the low-density fraction containing the plasma membrane and early endosomes, in addition to the dense lysosomes. LAMP-2B considerably existed in the low-density late endosomal fraction. These data strongly suggest that the LAMP-2 isoforms are distributed differently in endocytic organelles depending on their interaction strengths with AP-3.

Phytochelatin-Mediated Cultivar-Dependent Cd Accumulations of Lactuca sativa and Implication for Cd Pollution-Safe Cultivars Screening

Cd pollution-safe cultivar (Cd-PSC) is a feasible strategy to minimize Cd contamination in leafy vegetables. The shoot Cd concentrations of 23 Lactuca sativa cultivars under Cd stress ranged from 0.124 to 2.155 mg·kg-1 with a maximum cultivar difference of 8 folds. Typical Cd-PSC C16 (L) and high-Cd-accumulating cultivar C13 (H) were screened to investigate the mechanisms of Cd accumulations in L. sativa through determining Cd concentrations, Cd subcellular distributions, phytochelatin profiles, and phytochelatin biosynthesis-related genes' expressions. Higher Cd distribution in a heat stable fraction in C13 (H) indicated that the high Cd accumulation trait of C13 (H) mainly depended on the Cd-phytochelatin complexes. Root phytochelatin concentrations were significantly elevated in C13 (H) (5.83 folds) than in C16 (L) (2.69 folds) (p < 0.05) under Cd stress. Significantly downregulated expressions of glutathione S-transferase rather than the regulation of phytochelatin synthesis genes in the root of C13 (H) might be responsible for sufficient glutathione supply for phytochelatins synthesis. These findings suggested that phytochelatin elevation in C13 (H) would favor the Cd root to shoot transportation, which provides new insights into the phytochelatin-related cultivar-dependent Cd accumulating characteristic in L. sativa.

Uptake, Translocation, and Subcellular Distribution of Strobilurin Fungicides in Cucumber (Cucumis sativa L.)

The absorption, transport, and subcellular distribution of strobilurin fungicides (azoxystrobin, pyraclostrobin, and trifloxystrobin) have been studied in cucumbers. Under hydroponic laboratory conditions, pyraclostrobin and trifloxystrobin mainly accumulated in cucumber roots whereas azoxystrobin accumulated in cucumber leaves. In the subcellular distribution experiment, azoxystrobin mainly accumulated as a soluble component. Pyraclostrobin and trifloxystrobin accumulated more in the organelles and cell walls. Azoxystrobin and pyraclostrobin enter the root primarily through the apoplast pathway, whereas trifloxystrobin enters the root through the symplastic pathway. Azoxystrobin can be transported in cucumber through anion and cation channels, whereas pyraclostrobin and trifloxystrobin can be transported only through anion channels. This study has great significance in evaluating environmental risks and food safety.

Interactive effect of 24-epibrassinolide and silicon on the alleviation of cadmium toxicity in rice (Oryza sativa L.) plants

Cadmium (Cd) pollution is a serious threat to food safety and human health. Minimization of Cd uptake and enhancing Cd tolerance in plants are vital to improve crop yield and reduce hazardous effects to humans. In this study, we investigate the effect of a synergistic system with phytohormone (24-Epibrassinolide, EBL) and silicon (Si) on Cd toxicity and accumulation of rice plants. The results revealed that Si, EBL and their combination rescued Cd-induced growth inhibition, as evidenced by the increased dry weight of root and shoot. The chlorophyll content and photosynthetic performance were improved. The activity of antioxidant enzymes (SOD, POD and CAT) was increased and oxidative stress was alleviated. More importantly, Cd content in root was decreased by 20.25%, 17.72% and 27.84%, while Cd content in shoot decreased by 21.17%, 16.47% and 25.88%, respectively. Moreover, Si, EBL and Si + EBL treatment enriched cell wall-bound Cd and reduced Cd toxicity to functional organelles. Meanwhile, the residual form of Cd was enriched and the highly toxic forms of Cd (inorganic and water-soluble Cd) were decreased. The joint application showed better effects than applying Si and EBL alone. Collectively, this study provides an effective way for Cd toxicity mitigation in rice plants.

Absorption, metabolism and distribution of carbosulfan in maize plants (Zea mays L.)

BACKGROUND

The insecticide carbosulfan is usually applied as a soil treatment or seed-coating agent, and so may be absorbed by crops and pose dietary risks. Understanding the uptake, metabolism and translocation of carbosulfan in crops is conducive to its safe application. In this study, we investigated the distribution of carbosulfan and its toxic metabolites in maize plants at both the tissue and subcellular levels, and explored the uptake and translocation mechanism of carbosulfan.

RESULTS

Carbosulfan was mainly taken up by maize roots via the apoplast pathway, was preferentially distributed in cell walls (51.2%-57.0%) and most (85.0%) accumulated in roots with only weak upward translocation. Carbofuran, the main metabolite of carbosulfan in maize plants, was primarily stored in roots. However, carbofuran could be upwardly translocated to shoots and leaves because of its greater distribution in root-soluble components (24.4%-28.5%) compared with carbosulfan (9.7%-14.5%). This resulted from its greater solubility compared with its parent compound. The metabolite 3-hydroxycarbofuran was found in shoots and leaves.

CONCLUSION

Carbosulfan could be passively absorbed by maize roots, mainly via the apoplastic pathway, and transformed into carbofuran and 3-hydroxycarbofuran. Although carbosulfan mostly accumulated in roots, its toxic metabolites carbofuran and 3-hydroxycarbofuran could be detected in shoots and leaves. This implies that there is a risk in the use of carbosulfan as a soil treatment or seed coating. © 2023 Society of Chemical Industry.

Differential Effects of Senescence on the Phloem Exports of Cadmium and Zinc from Leaves to Grains in Rice during Grain Filling

In rice, non-essential toxic cadmium (Cd) and the essential nutrient zinc (Zn) share similar transport pathways, which makes it challenging to differentially regulate the allocation of these elements to the grain. The phloem is the main pathway for the loading of these elements into rice grains. It has long been accepted that tissue senescence makes the nutrients (e.g., Zn) stored in leaves available for further phloem export toward the grain. Whether senescence could drive the phloem export of Cd remains unclear. To this end, the stable isotopes ¹¹¹Cd and ⁶⁷Zn were used to trace the phloem export and the subsequent allocation of Cd and Zn from the flag leaves, where senescence was accelerated by spraying abscisic acid. Furthermore, changes upon senescence in the distribution of these elements among the leaf subcellular fractions and in the expression of key transporter genes were investigated. Abscisic acid-induced senescence enhanced the phloem export of Zn but had no impact on that of Cd, which was explained by the significant release of Zn from the chloroplast and cytosol fractions (concentrations decreased by ~50%) but a strong allocation of Cd to the cell wall fraction (concentration increased by ~90%) during senescence. Nevertheless, neither Zn nor Cd concentrations in the grain were affected, since senescence strengthened the sequestration of phloem-exported Zn in the uppermost node, but did not impact that of phloem-exported Cd. This study suggests that the agronomic strategies affecting tissue senescence could be utilized to differentially regulate Cd and Zn allocation in rice during grain filling.

A Dark Septate Endophyte Improves Cadmium Tolerance of Maize by Modifying Root Morphology and Promoting Cadmium Binding to the Cell Wall and Phosphate

Dark septate endophytes (DSEs) can improve the performance of host plants grown in heavy metal-polluted soils, but the mechanism is still unclear. A sand culture experiment was performed to investigate the effects of a DSE strain (Exophiala pisciphila) on maize growth, root morphology, and cadmium (Cd) uptake under Cd stress at different concentrations (0, 5, 10, and 20 mg·kg^-1). The results indicated that the DSE significantly improved the Cd tolerance of maize, causing increases in biomass, plant height, and root morphology (length, tips, branch, and crossing number); enhancing the Cd retention in roots with a decrease in the transfer coefficient of Cd in maize plants; and increasing the Cd proportion in the cell wall by 16.0-25.6%. In addition, DSE significantly changed the chemical forms of Cd in maize roots, resulting in decreases in the proportions of pectates and protein-integrated Cd by 15.6-32.4%, but an increase in the proportion of insoluble phosphate Cd by 33.3-83.3%. The correlation analysis revealed a significantly positive relationship between the root morphology and the proportions of insoluble phosphate Cd and Cd in the cell wall. Therefore, the DSE improved the Cd tolerance of plants both by modifying root morphology, and by promoting Cd binding to the cell walls and forming an insoluble phosphate Cd of lower activity. These results of this study provide comprehensive evidence for the mechanisms by which DSE colonization enhances Cd tolerance in maize in root morphology with Cd subcellular distribution and chemical forms.

Effects of Culinary Procedures on Concentrations and Bioaccessibility of Cu, Zn, and As in Different Food Ingredients

Although cooked diets are the primary sources for humans to absorb trace elements, there is limited data available on the concentrations and bioaccessibility of trace elements in cooked food ingredients. This work aims to evaluate the effects of culinary procedures on the concentrations and bioaccessibility of trace elements in common food ingredients. Twelve food species from the local market were treated with four culinary procedures (boiling, steaming, baking, and frying), then the bioaccessibility of copper (Cu), zinc (Zn), and arsenic (As) were evaluated using the in vitro digestion method. The subcellular distribution of these elements was also determined using the sequential fractionation method. The results show that culinary procedures decreased the retention rate of As during cooking (100% for raw and 65-89% for cooked ingredients) and the bioaccessibility of Cu and Zn during digestion (nearly 75% for raw and 49-65% for cooked ingredients), resulting in a reduction of the total bioaccessible fraction (TBF) of Cu, Zn, and As in food ingredients. The TBF of Cu, Zn, and As in all tested food ingredients followed the order: raw (76-80%) > steaming and baking (50-62%) > boiling and frying (41-50%). The effects of culinary procedures were associated with the subcellular distribution of trace elements. As was dominantly distributed in heat-stable proteins (51-71%), which were more likely to be lost during cooking. In comparison, Cu and Zn were mainly bound to the insoluble fraction and heat-denatured proteins (60-89% and 61-94% for Cu and Zn, respectively), which become less digestible in cooked ingredients. In conclusion, these results suggest that culinary procedures reduce the absorption of Cu, Zn, and As in various food ingredients, which should be considered in the coming studies related to nutrition and risk assessment of trace elements.

A novel gene SpCTP3 from the hyperaccumulator Sedum plumbizincicola redistributes cadmium and increases its accumulation in transgenic Populus × canescens

A cadmium (Cd) tolerance protein (SpCTP3) involved in the Sedum plumbizincicola response to Cd stress was identified. However, the mechanism underlying the Cd detoxification and accumulation mediated by SpCTP3 in plants remains unclear. We compared wild-type (WT) and SpCTP3-overexpressing transgenic poplars in terms of Cd accumulation, physiological indices, and the expression profiles of transporter genes following with 100 μmol/L CdCl₂. Compared with the WT, significantly more Cd accumulated in the above-ground and below-ground parts of the SpCTP3-overexpressing lines after 100 μmol/L CdCl₂ treatment. The Cd flow rate was significantly higher in the transgenic roots than in the WT roots. The overexpression of SpCTP3 resulted in the subcellular redistribution of Cd, with decreased and increased Cd proportions in the cell wall and the soluble fraction, respectively, in the roots and leaves. Additionally, the accumulation of Cd increased the reactive oxygen species (ROS) content. The activities of three antioxidant enzymes (peroxidase, catalase, and superoxide dismutase) increased significantly in response to Cd stress. The observed increase in the titratable acid content in the cytoplasm might lead to the enhanced chelation of Cd. The genes encoding several transporters related to Cd²⁺ transport and detoxification were expressed at higher levels in the transgenic poplars than in the WT plants. Our results suggest that overexpressing SpCTP3 in transgenic poplar plants promotes Cd accumulation, modulates Cd distribution and ROS homeostasis, and decreases Cd toxicity via organic acids. In conclusion, genetically modifying plants to overexpress SpCTP3 may be a viable strategy for improving the phytoremediation of Cd-polluted soil.

Salicylic Acid Enhances Cadmium Tolerance and Reduces Its Shoot Accumulation in Fagopyrum tataricum Seedlings by Promoting Root Cadmium Retention and Mitigating Oxidative Stress

Soil cadmium (Cd) contamination seriously reduces the production and product quality of Tartary buckwheat (Fagopyrum tataricum), and strategies are urgently needed to mitigate these adverse influences. Herein, we investigated the effect of salicylic acid (SA) on Tartary buckwheat seedlings grown in Cd-contaminated soil in terms of Cd tolerance and accumulation. The results showed that 75-100 µmol L^-1 SA treatment enhanced the Cd tolerance of Tartary buckwheat, as reflected by the significant increase in plant height and root and shoot biomass, as well as largely mitigated oxidative stress. Moreover, 100 µmol L^-1 SA considerably reduced the stem and leaf Cd concentration by 60% and 47%, respectively, which is a consequence of increased root biomass and root Cd retention with promoted Cd partitioning into cell wall and immobile chemical forms. Transcriptome analysis also revealed the upregulation of the genes responsible for cell wall biosynthesis and antioxidative activities in roots, especially secondary cell wall synthesis. The present study determines that 100 µmol L^-1 is the best SA concentration for reducing Cd accumulation and toxicity in Tartary buckwheat and indicates the important role of root in Cd stress in this species.

Subcellular distribution and chemical forms of manganese in Daucus carota in relation to its tolerance

Daucus carota is a biennial herb of the Umbelliferae family, which is a candidate plant for the phytoremediation of Mn pollution. To reveal the mechanism of this plant to adapt to Mn stress, plant growth, anatomical structure, Mn accumulation characteristic, Mn subcellular distribution, and chemical forms of D. carota under six Mn²⁺ concentrations by pot culture experiments were studied. The results showed that with the rising Mn concentrations, the total dry weight and leaf area of D. carota increased firstly and then decreased, while the specific leaf area increased. The thickness of the main vein, upper epidermis, and lower epidermis; the thickness of the palisade tissue; and the thickness of the spongy tissue of the leaves increased firstly and then decreased. The Mn content in the aboveground and underground parts of D. carota increased, and the values of the bioconcentration factor (BCF) and translocation factor (TF) were higher than 1. The Mn existing in the cell wall and soluble components accounted for the largest proportion, and the proportion of Mn in the cell wall increased with increasing concentrations of Mn. In addition, Mn mainly existed in ethanol extraction state, deionized water extraction state, and sodium chloride extraction state. The results showed that D. carota could alleviate the damage caused by high manganese concentration by storing most of manganese in the cell wall and vacuole and existing in the form of low-activity state.

Sulfur reduces the root-to-shoot translocation of arsenic and cadmium by regulating their vacuolar sequestration in wheat (Triticum aestivum L.)

Accumulation of arsenic (As) and cadmium (Cd) in wheat grain is a serious threat to human health. Sulfur (S) can simultaneously decrease wheat grain As and Cd concentrations by decreasing their translocation in wheat; however, the mechanisms are unclear. We conducted hydroponic experiments to explore the mechanisms by which S modulates As and Cd translocation and their toxicity in wheat. Wheat seedlings were grown in deficient sulfate (2.5 µM) or sufficient sulfate (1.0 mM) nutrient solutions for 6 days and then exposed to zero (control), low As+Cd (1 µM As plus 0.5 µM Cd), or high As+Cd (50 µM As plus 30 µM Cd) for another 6 days. Compared with the control, plant growth was not affected by low As+Cd, but was significantly inhibited by high As+Cd. In the low As+Cd treatment, S supply had no significant effect on plant growth or root-to-shoot As and Cd translocation. In the high As+Cd treatment, sufficient S supply significantly alleviated As and Cd toxicity and their translocation by increasing phytochelatin (PC) synthesis and the subsequent vacuolar sequestration of As and Cd in roots, compared with deficient S supply. The use of _L-buthionine sulfoximine (a specific inhibitor of γ-glutamylcysteine synthetase) confirmed that the alleviation of As and Cd translocation and toxicity in wheat by S is mediated by increased PC production. Also, TaHMA3 gene expression in wheat root was not affected by the As+Cd and S treatments, but the expression of TaABCC1 was upregulated by the high As+Cd treatment and further increased by sufficient S supply and high As+Cd treatment. These results indicate that S-induced As and Cd subcellular changes affect As and Cd translocation mainly by regulating thiol metabolism and ABCC1 expression in wheat under As and Cd stress.

[Effects of Exogenous Jasmonic Acid on Arsenic Accumulation and Response to Stress in Roots of Rice Seedlings]

Arsenic (As) pollution has a toxic effect on crop growth, leading to reduced crop quality and yield. Therefore, it is urgent to explore safe and effective strategies to reduce its toxicity. In this experiment, hydroponics, fluorescent probe locating technology, differential centrifugation, and Fourier infrared spectroscopy (FTIR) analysis were used to research the effect of exogenous jasmonic acid (JA) on the accumulation and stress resistance of rice seedlings. The results showed that JA application reduced the As content in the roots and shoots of rice by 31.4% and 51.4%, respectively, and significantly reduced As content in the cell wall and soluble fractions of rice roots. JA changed the distribution ratio of As in the subcellular components. The distribution ratio of As in the cell wall increased by 16.4%, and the distribution ratio of soluble fractions decreased by 17.3%. JA enhanced the fixation of As by the cell wall and reduced the As content in the soluble fraction. Furthermore, JA increased the levels of SOD, CAT, GSH, and PEPC in root cells and reduced the contents of H₂O₂ and MDA, indicating that JA reduced lipid peroxidation damage, regulated carbon and nitrogen metabolism, and alleviated As toxicity. This research provides a new approach for the prevention and control of rice As pollution.

Dynamic and Comparative Transcriptome Analyses Reveal Key Factors Contributing to Cadmium Tolerance in Broomcorn Millet

Broomcorn millet (Panicum miliaceum L.) has great potential in Cd phytoextraction, but its mechanisms are largely unknown. Two contrasting broomcorn millet varieties, 'Ningmi6' (Cd-sensitive variety) and '4452' (Cd-tolerant variety), were investigated through morphological, physiological, and transcriptomic analyses to determine the factors responsible for their differential Cd tolerance and translocation. The Cd-tolerant variety can accumulate more Cd, and its cell wall and vacuole component Cd proportions were higher compared with the Cd-sensitive variety. Under Cd stress, the glutathione content and peroxidase activity of the Cd-tolerant variety were significantly higher than those of the Cd-sensitive variety. Additionally, weighted gene co-expression network analysis (WGCNA) revealed hub modules that were associated with Cd stress and/or variety. Notably, genes involved in these hub modules were significantly enriched for roles in glutathione metabolism, phenylpropanoid biosynthesis, ABC transport, and metal ion transport process. These results suggested that regulation of genes associated with cell wall precipitation and vacuole compartmentalization may increase Cd tolerance and reduce Cd translocation in the Cd-tolerant variety, although it can absorb more Cd. This study provides a foundation for exploring molecular mechanisms of Cd tolerance and transport in broomcorn millet and new insights into improving Cd phytoremediation with this crop through genetic engineering.

New insights in copper handling strategies in the green alga Chlamydomonas reinhardtii under low-iron condition

Copper (Cu) is a redox-active transition element critical to various metabolic processes. These functions are accomplished in tandem with Cu binding ligands, mainly proteins. The main goal of this work was to understand the mechanisms that govern the intracellular fate of Cu in the freshwater green alga, Chlamydomonas reinhardtii, and more specifically to understand the mechanisms underlying Cu detoxification by algal cells in low-Fe conditions. We show that Cu accumulation was up to 51-fold greater for algae exposed to Cu in low-Fe medium as compared to the replete-Fe growth medium. Using the stable isotope 65Cu as a tracer, we studied the subcellular distribution of Cu within the various cell compartments of C. reinhardtii. These data were coupled with metallomic and proteomic approaches to identify potential Cu-binding ligands in the heat-stable protein and peptide fractions of the cytosol. Cu was mostly found in the organelles (78%), and in the heat-stable proteins and peptides (21%) fractions. The organelle fraction appeared to also be the main target compartment of Cu accumulation in Fe-depleted cells. As Fe levels in the medium were shown to influence Cu homeostasis, we found that C. reinhardtii can cope with this additional stress by utilizing different Cu-binding ligands. Indeed, in addition to expected Cu-binding ligands such as glutathione and phytochelatins, 25 proteins were detected that may also play a role in the Cu detoxification processes in C. reinhardtii. Our results shed new light on the coping mechanisms of C. reinhardtii when exposed to environmental conditions that induce high rates of Cu accumulation.

Magnesium absorption, translocation, subcellular distribution and chemical forms in citrus seedlings

Magnesium (Mg) is an essential macronutrient for plant growth and development; however, the adaptive mechanisms of Mg deficiency to underlying changes in Mg translocation, subcellular distribution and chemical forms in citrus plants are unknown. In this study, we conducted a sand culture experiment with 0 (Mg-deficiency) or 2 (Mg-sufficiency) mmol l-1 Mg2+ treatments to investigate the responses underlying Mg adaptability, as well as the resulting growth and Mg transport features in citrus seedlings [Citrus sinensis (L.) Osbeck cv. 'Xuegan']. We found that Mg-deficiency significantly depressed biomass by 39% in the whole plant and by 66% in branch organs compared with Mg-sufficient conditions, which further resulted in a subsequent decrease in Mg concentration and accumulation with changes in its distribution in different organs and a reduction in root growth. Under Mg-sufficiency, >50% of Mg was sequestered in the soluble fraction and this was reduced by 30% under Mg-deficiency. Furthermore, >70% of Mg existed as inorganic (42%) and water-soluble (31%) forms with high mobility across treatments and organs. Under Mg-deficiency, the proportion of water-soluble Mg was reduced in leaf and increased in root, whereas the proportion of inorganic Mg increased in main stem leaves and decreased in branch leaves and root. However, under Mg-deficiency, the proportion of Mg forms with low mobility, including pectates and proteins, phosphates, oxalates and residues, was increased in leaf and root organs, with the exception of pectate and protein Mg, which was decreased in root. The Mg transfer factor showed that Mg-deficiency improved Mg transport from parent to branch organs, which was related to Mg subcellular distribution and chemical forms. Taken together, our study establishes a defined process to clarify the mechanisms of Mg absorption and translocation and reveals a possible strategy to effectively improve Mg mobility and availability in citrus plants.

Effect of Fungal Endophyte Epichloë bromicola Infection on Cd Tolerance in Wild Barley (Hordeum brevisubulatum)

Hydroponic Hordeum brevisubulatum (wild barley) was used as material in the greenhouse to study the effects of endophyte infection on plant growth, Cd absorption and transport, subcellular distribution, and Cd chemical forms under CdCl2 stress. Endophytic fungi respond positively to chlorophyll content and photosynthetic efficiency under Cd stress. The order of Cd absorption in different parts of the plant was: roots > stems > leaves. Endophyte infection increased the plant’s absorption and transport of Cd while causing a significant difference in the stem, which was associated with the distribution density of endophyte hyphae. The proportion of organelle Cd in endophyte-infected wild barley was significantly higher, which facilitated more Cd transport to aboveground. Cd stress showed a slight effect on the chemical forms of Cd in leaves. The proportion of phosphate, oxalate, and residual Cd increased in the stem. Cd existed in the form of inorganic salt, organic acid, pectin, and protein in roots. Endophyte infection reduced the Cd content of the more toxic chemical forms to protect the normal progress of plant physiological functions. Therefore, the isolation of cell walls and vacuoles is a key mechanism for plant Cd tolerance and detoxification. As endophyte infections have more ability to absorb Cd in plants, H. brevisubulatum−Epichloë bromicola symbionts can improve heavy metal contaminated soil and water.

Foliar Spraying of Selenium Combined with Biochar Alleviates Cadmium Toxicity in Peanuts and Enriches Selenium in Peanut Grains

Cadmium (Cd) pollution in soil, particularly in peanut production, is a problem that has attracted global concern and needs solutions urgently. Selenium (Se) can alleviate Cd toxicity; however, the underlying mechanisms are not completely understood. Therefore, two varieties of peanut (Arachis hypogaea Linn.), “Huayu 23” and “Huayu 20”, were chosen as the target crops for this study. A pot experiment was conducted to investigate the effects of two Se application methods combined with biochar on the accumulation of Cd and Se, and the best application method was identified. In addition, the role of Se in alleviating Cd toxicity in peanuts was studied. The results indicated that both Se and biochar decreased the Cd content in peanuts and alleviated Cd toxicity. However, the combined application of foliar Se and biochar significantly increased the peanut biomass by 73.44–132.41%, increased the grain yield of Huayu 23 by 0.60–1.09 fold, and Huayu 20 by 2.38–3.48 fold. Additionally, Cd content in peanut grains was decreased by 32.81–50.07%, and Se content was increased by 31.57–99.75 folds. Biochar can decrease the absorption of Cd from the soil, while Se can increase the accumulation of Cd in cell vacuoles by increasing glutathione and phytochelatin to decrease the movement of Cd into the grains. Therefore, our results indicate that the combined application of foliar Se and biochar can effectively promote the enrichment of Se in peanuts and suppress Cd toxicity.

Accumulation Mechanism and Risk Assessment of Artemisia selengensis Seedling In Vitro with the Hydroponic Culture under Cadmium Pressure

Artemisia selengensis is a perennial herb of the Compositae with therapeutic and economic value in China. The cadmium (Cd) accumulation mechanism and healthy risk evaluation of A. selengensis were investigated in this study. Tissue culture seedlings were obtained by plant tissue culture in vitro, and the effect of Cd stress (Cd concentration of 0.5, 1, 5, 10, 25, 50 and 100 μM) on A. selengensis was studied under hydroponic conditions. The results showed that low-Cd (0.5–1 μM) stress caused a rare effect on the growth of A. selengensis seedlings, which regularly grew below the 10 μM Cd treatment concentration. The biomass growth rate of the 0.5, 1, and 5 μM treatment groups reached 105.8%, 96.6%, and 84.8% after 40 days of cultivation, respectively. In addition, when the concentration of Cd was greater than 10 μM, the plant growth was obviously inhibited, i.e., chlorosis of leaves, blackening roots, destroyed cell ultrastructure, and increased malondialdehyde (MDA) content. The root could be the main location of metal uptake, 57.8–70.8% of the Cd was concentrated in the root after 40 days of cultivation. Furthermore, the root cell wall was involved in the fixation of 49–71% Cd by subcellular extraction, and the involvement of the participating functional groups of the cell wall, such as -COOH, -OH, and -NH₂, in metal uptake was assessed by FTIR analysis. Target hazard quotient (THQ) was used to assess the health risk of A. selengensis, and it was found that the edible part had no health risk only under low-Cd stress (0.5 to 1 μM) and short-term treatment (less than 20 days).

Subcellular Distribution of Dietary Methyl-Mercury in Gammarus fossarum and Its Impact on the Amphipod Proteome

The transfer of methyl-Hg (MeHg) from food is central for its effects in aquatic animals, but we still lack knowledge concerning its impact on invertebrate primary consumers. In aquatic environments, cell walls of plants are particularly recalcitrant to degradation and as such remain available as a food source for long periods. Here, the impact at the proteomic level of dietary MeHg in Gammarus fossarum was established and linked to subcellular distribution of Hg. Individuals of G. fossarum were fed with MeHg in cell wall or intracellular compartments of Elodea nuttallii. Hg concentrations in subcellular fractions were 2 to 6 times higher in animals fed with cell wall than intracellular compartments. At the higher concentrations tested, the proportion of Hg in metal-sensitive fraction increased from 30.0 ± 6.1 to 41.0 ± 5.7% for individuals fed with intracellular compartment, while biologically detoxified metal fraction increased from 30.0 ± 6.1 to 50.0 ± 2.8% when fed with cell wall compartment. Data suggested that several thresholds of proteomic response are triggered by increased bioaccumulation in each subcellular fraction in correlation with Hg exclusively bound to the metal-sensitive fraction, while the increase of biologically detoxified metal likely had a cost for fitness. Proteomics analysis supported that the different binding sites and speciation in shoots subsequently resulted in different fate and cellular toxicity pathways to consumers. Our data confirmed that Hg bound in cell walls of plants can be assimilated by G. fossarum, which is consistent with its feeding strategy, hence pointing cell walls as a significant source for Hg transfers and toxicity in primary consumers. The high accumulation of Hg in macrophytes makes them a risk for food web transfer in shallow ecosystems. The present results allowed gaining new insights into the effects and uptake mechanisms of MeHg in aquatic primary consumers.

Role of Toxicokinetic and Toxicodynamic Parameters in Explaining the Sensitivity of Zebrafish Larvae to Four Metals

Given the persistence and toxic potencies of metal contaminants in ecosystems, animals, and human beings, they are considered to be hazardous global pollutants. While the lethality of metal toxicities (e.g., LC₅₀) can significantly vary, even within the same species, the underlying mechanisms are less well-understood. In this study, we developed a subcellular two-compartment toxicokinetic-toxicodynamic (TK-TD) model for zebrafish larvae when exposed to four metals (cadmium, lead, copper, and zinc) to reveal whether differences in metal toxicity (LC₅₀ values) were dominated by the TK or TD processes. Results showed that the subcellular TK and TD parameters of the four metals were significantly different, and the bioconcentration factor (BCF) value of copper was higher than those of the other metals. We also found that the TD parameter internal threshold concentration (C_IT) was significantly positively correlated to the LC₅₀ values (R² = 0.7), suggesting a dominant role of TD processes in metal toxicity. Furthermore, the combined parameter C_IT/BCF for a metal-sensitive fraction (BCF_MSF), which linked exposure to effects through the TK-TD approach, explained up to 89% of the variation in toxicity to the four metals. The present study suggests that the observed variation in toxicity of these four metals was mainly determined by TD processes but that TK processes should not be ignored, especially for copper.

NanoSIMS Imaging of Bioaccumulation and Subcellular Distribution of Manganese During Oyster Gametogenesis

Many bivalve mollusks display remarkable sex differentiation of gonadal accumulation of manganese (Mn), but the underlying processes responsible for such differences have seldom been explored. In this study, the accumulation of Mn in male and female gonads during the reproductive cycle of oysters was first examined, and the distributions of Mn in oocytes and sperm cells at different developmental stages were imaged by the nanoscale secondary ion mass spectrometry (NanoSIMS) at the subcellular level. We found that the distribution and accumulation of Mn during oogenesis were closely associated with the formation and translocation of cortical granules. This is the first time that the enrichment of Mn was directly visualized in cortical granules, which was identified as the major storage site of Mn in oocytes of oysters. Yolk granules were revealed as another storage pool of Mn in oyster oocytes with lower accumulation. In contrast, Mn was mainly distributed in the nucleus of sperm cells with accumulation levels much lower than those in cortical and yolk granules of oocytes. These results demonstrated great differences of the subcellular localization and accumulation capacity of Mn between oocytes and sperm cells in oysters, implying the sex differentiation in susceptibility of reproductive response to Mn stress. Our study also highlights the importance of gender difference in future biomonitoring and ecotoxicological studies of Mn in marine bivalves.

Accumulation and subcellular distribution of cadmium in rygegrass induced by Aspergillus niger TL-F2 and Aspergillus flavus TL-F3

Although plant growth-promoting fungi can greatly accelerate the ryegrass bioaccumulation of cadmium (Cd), the underlying mechanisms are not yet well documented. Therefore, we performed a 20-days hydroponic experiment to investigate the effects of Aspergillus niger TL-F2 (A. niger TL-F2) and Aspergillus flavus TL-F3 (A. flavus TL-F3) on accumulation/subcellular distribution of Cd by annual ryegrass Dongmu 70 at different Cd concentrations (0, 2.5, and 5 mg L^-1). Results indicated that both fungal strains promoted ryegrass biomass/growth by about 60%. Furthermore, we found that ryegrass roots (17.8-37.1 μg pot^-1) had a significantly higher capability for Cd uptake than the shoots (1.66-5.45 μg pot^-1) (p < 0.05). Of total Cd in ryegrass plants, 44-67% was in soluble form, 24-37% was in cell wall, and 8.5-25.5% was in organelles. Compared with non-fungus ryegrass, cell wall and soluble Cd fractions in fungus-inoculated roots increased and decreased by 13.5-44% and 21.5-26.4%, respectively. Besides, fungus inoculation generally increased the content of cell wall and soluble Cd fractions in ryegrass shoots. Altogether, the study concludes that inoculation of fungus in ryegrass is a promising approach to improve phytoremediation of Cd contaminated environments.Novelty statement Previous study by Han et al. (2018) examined the resistance of ryegrass plant to Cd stress after its inoculation with Aspergillus aculeatus. In this study, using a hydroponic experiment, we examined the effects of co-application of two species of Aspergillus fungi. i.e. A. niger TL-F2 and A. flavus TL-F3 on ryegrass growth/biomass, Cd absorption by ryegrass shoots and roots, and subcellular distribution of Cd in ryegrass roots and shoots.

Uptake, Accumulation, Translocation, and Subcellular Distribution of Perchlorate in Tea (Camellia sinensis L.) Plants

Perchlorate, emerging pollution with thyroid toxicity, has a high detection rate in fresh tea leaves. What needs attention is that the uptake characteristic is insufficiently understood. Herein, the uptake, accumulation, and translocation of perchlorate in a tea plant-hydroponic solution system were investigated, of which the mechanism was further lucubrated by subcellular distribution. The perchlorate concentration in tea tissues is ramped up along with the increase in the exposure level and time. The bioaccumulation factor of tea tissues followed the rank: mature leaves > tender leaves > roots. After the seedlings have been transplanted to a perchlorate-free solution, the perchlorate in mature leaves is reduced significantly, accompanied by a progressive increase in perchlorate in new shoots and solutions. The cell-soluble fractions are the major reservoir of perchlorate both for roots (>59%) and leaves (>76%), which precisely explained the translocation within the tea plant-hydroponic solution system. These results not only illuminate the uptake characteristic in tea plants but also improve the understanding of the behavior of perchlorate in higher plants.

[Comparison of Enrichment and Transport of Cadmium in the Fruit of High and Low Enrichment Pepper Varieties and Its Distribution in Subcells]

Peppers are a high Cd-enriched vegetable. On the basis of a preliminary screening experiment of 91 pepper varieties and soil culture experiments during the entire growth period of 26 varieties, a high Cd variety (X15), medium Cd variety (X39), and two low varieties (X45 and X55) were selected to study the effect of different cadmium levels (0, 5, and 10 mg·kg^-1 Cd) on enrichment, transport, and accumulation as well as its subcellular distribution and chemical form. Based on the results, 5 mg·kg^-1 and 10 mg·kg^-1 of Cd inhibited shoot dry weights of four pepper varieties but increased the root dry weights of X15, X45, and X55 varieties. Sodium chloride-bound cadmium and acetate-bound cadmium are the main forms of cadmium in the pepper fruits. Subcellular cadmium concentrations in the roots, leaves, and fruits of pepper plants were ranked in order cytoplasm > cell wall > organelle, and in the stems the order was cell wall > cytoplasm > organelle. Cd compartmentalization plays an important role in pepper resistance to cadmium stress. Under dosages of 5 mg·kg^-1 Cd and 10 mg·kg^-1 Cd, Cd concentrations in stems and leaves were ranked in order X39 > X15 > X55 > X45, with fruit Cd concentrations ranked in order X15 > X39 > X55 > X45. The Cd concentration was lowest in the roots of X15 whereas this variety has the highest concentrations in its fruit. The Cd concentrations in the roots, stems, and leaves of X39 were the highest among the four varieties whereas the concentration in the fruit was lower than in the X15 variety. The concentration of Cd in pepper fruits depends on the Cd transport capacity redistribution ability to the shoots.

Identification and In Vitro Functional Verification of Two Novel Mutations of GHR Gene in the Chinese Children with Laron Syndrome

PURPOSE

Laron syndrome (LS) is a severe growth disorder caused by GHR gene mutation or post-receptor pathways defect. The clinical features of these patients collected in our present study were summarized, GHR gene variants were investigated and further in vitro functional verification was carried out.

METHODS

Four patients with LS were collected, their clinical characteristics were summarized, genomic DNA was extracted, and GHR gene was amplified and sequenced. GHR wild type (GHR-WT) and mutant GHR expression plasmids were constructed, and transiently transfected into HepG2 cells and HEK293T cells to observe the subcellular distribution of the GHR protein by immunofluorescence and to determine the expression of GHR and its post-receptor signaling pathway changes by Western blotting.

RESULTS

All of the four patients were male, and the median height was -4.72 SDS. Four GHR gene variants including c.587A>C (p.Y196S), c.766C>T (p.Q256*), c.808A>G (p.I270V) and c.1707-1710del (p.E570Afs*30) were identified, and the latter two were novel mutations. The results of mutant GHR plasmids transfection experiments and immunofluorescence assay showed that the subcellular distribution of GHR-Q256* and GHR-E570Afs*30 mutant proteins in HepG2 and HEK293T cells presented with a unique ring-like pattern, gathering around the nucleus, while GHR-Y196S mutant protein was evenly distributed on HepG2 cell membrane similar to GHR-WT. The GHR protein levels of HepG2 cells transiently transfected with GHR-Y196S, GHR-Q256* and GHR-E570Afs*30 were all significantly lower when compared with cells transfected with GHR-WT (P<0.05). Further mutant GHR post-receptor signal transduction investigation demonstrated that GH induced phosphorylated STAT5 levels of HepG2 cells transfected with three mutant plasmids were all significantly decreased in comparison with that of GHR-WT (P<0.05).

CONCLUSIONS

Two novel GHR gene mutations (I270V and E570Afs*30) were found in our patients with LS. GHR mutations influenced the subcellular distribution and GHR protein levels, then led to the impaired post-receptor signal transduction, suggesting that the GHR mutations contributed to the pathological condition of LS patients.

Exogenous Glutathione Alleviation of Cd Toxicity in Italian Ryegrass (Lolium multiflorum) by Modulation of the Cd Absorption, Subcellular Distribution, and Chemical Form

Subcellular fractions and the chemical forms of cadmium (Cd) reflect its level of toxicity to plants; however, these effects of exogenous glutathione (GSH) are poorly understood. We exposed two Italian ryegrass (Lolium multiflorum) cultivars (IdyII and Harukaze) to 50 µM Cd or 200 µM GSH to investigate the effect of GSH on the Cd uptake, subcellular compartments, and chemical forms. Cd significantly inhibited the plant growth, while GSH supplementation decreased this inhibition. The application of GSH significantly improved the Cd concentration in the roots but reduced that in the shoots and decreased the Cd translocation from root to shoot. The Cd concentration of the root in the cell wall was increased while the concentration in the soluble fraction was decreased when supplied with GSH. The inorganic form (80% ethanol for Cd extraction) in the roots was significantly reduced when treated with GSH. The Cd form extracted by 2% acetic acid (HAC) with low toxicity and immobility were greatly increased. In leaves, the application GSH decreased in any form of Cd form extracted. In conclusion, exogenous GSH decreased the translocation of Cd and alleviated Italian ryegrass Cd toxicity by accumulating more Cd in the root cell wall and immobilizing more Cd in lower toxicity fractions.

Foliar uptake and transport of atmospheric trace metals bounded on particulate matters in epiphytic Tillandsia brachycaulos

Epiphytic Tillandsia species are uniquely suitable for the study of foliar uptake of atmospheric trace metals (ATM) because these plants can only rely on their leaves for this purpose. Therefore, we analyzed the uptake and transport of different metals (Fe, Al, Zn, Mn, Ba, Ti, Cu, Ni, Cr, Sn, Pb, Co, As, and Se) bounded on atmospheric particulate matters (APM) in Tillandsia brachycaulos Schltdl. The results showed that the metal contents inside leaves significantly (p < .05) increased after APM exposure. There was a significant (p < .05) positive correlation between the content of 14 trace metals accumulated on the leaf surface and inside the leaf, which indicated that APM is the main source of ATM uptake. The subcellular analysis showed that the Pb, Cu, Ni, Zn, and Cr absorbed by T. brachycaulos were stored primarily in the cell walls and organelles. After the removal of foliar trichomes of T. brachycaulos, the metal contents on the leaf surface decreased, whereas the contents of most metals inside the leaf increased. This is an evidence that foliar trichomes serve a protective function by intercepting ATM onto the leaf surface.Novelty statementsThere was a significant positive correlation between the contents of 14 trace metals accumulated on the leaf surface and in the leaf of T. brachycaulos, which indicated that atmospheric particulate matters are the main source of trace metals in the leaves.After the removal of foliar trichomes of T. brachycaulos, the trace metal contents on the leaf surface decreased, whereas the contents of most trace metals inside the leaf increased. This is an evidence that foliar trichomes serve a protective function by intercepting atmospheric trace metals onto the leaf surface.

Selenium Enhances Cadmium Accumulation Capability in Two Mustard Family Species-Brassica napus and B. juncea

Oilseed rape (Brassica napus) is a Cadmium (Cd) hyperaccumulator. However, high-level Cd at the early seedling stage seriously arrests the growth of rape, which limits its applications. Brassica juncea had higher Cd accumulation capacity, but its biomass was lower, also limiting its applications. Previous studies have confirmed that Selenium (Se) can alleviate Cd toxicity. However, the regulatory mechanism of Se in different valence states of Cd accumulation was unclear. In this study, we investigated the ameliorating effects of three Se valence states, Na₂SeO₄ [Se(VI)], Na₂SeO₃ [Se(IV)] and Se-Met [Se(II)], to Cd toxicity by physiological and biochemical approaches in hydroponically-cultured Brassica juncea and Brassica napus seedlings. Although Se treatments slightly inhibited seedling Cd concentration, it tripled or quadrupled the Cd accumulation level per plant, because dry weight increased about four times more with Se and Cd application than with Cd treatment alone. Among the different valence states of Se, Se(II) had the most marked effect on reducing Cd toxicity as evidenced by decreased growth inhibition and Cd content. The application of Se(II) was effective in reducing Cd-induced reactive oxygen species accumulation, and promoted the antioxidant enzyme activity and photosynthesis of both Brassica species. In addition, Se(II) treatment increased the concentrations of Cd in the cell wall and soluble fractions, but the Cd concentration in the organelle part was reduced.

Selenite Uptake and Transformation in Rice Seedlings (Oryza sativa L.): Response to Phosphorus Nutrient Status

Selenite and phosphate share similar uptake mechanisms, as a phosphate transporter is involved in the selenite uptake process. However, the mechanism by which selenium (Se) transformation in plants is mediated by phosphorus (P) remains unclear. In this hydroponic study, the absorption, translocation, and biotransformation of Se in selenite-treated rice (Oryza sativa L.) seedlings were investigated under varying P nutrient status. The results showed that P-deficient cultivation increased the Se concentration in roots with Se-only treatment by 2.1 times relative to that of the P-normal condition. However, co-treating roots with additional P caused the Se concentration to decline by 20 and 73% compared to Se treatment alone under P-normal and P-deficient cultivation, respectively. A similar pattern was also observed in Se uptake by rice roots. With an Se-transfer factor elevated by 4.4 times, the shoot Se concentration was increased by 44% with additional P supply compared to the concentration under Se-only treatment of P deficiency; however, no significant differences were observed regarding P-normal cultivation. P deficiency increased the Se percentage by 28% within the cell wall, but reduced it by 60% in the soluble fraction of Se-only treated roots relative to that of the P-normal condition. Contrarily, compared with the Se-only treatment under P deficiency, additional P supply enhanced Se storage in the root soluble fraction by 1.3 times. The opposite tendency was observed for rice shoots. Moreover, P deficiency reduced the proportion of SeMet by 22%, but increased MeSeCys by 1.3 times in Se-only treated roots compared to those under the P-normal condition. Interestingly, MeSeCys was not detected when additional P was added to the two cultivation conditions. Unlike in the roots, only SeMet was generally detected in the rice shoots. The results demonstrate that the P nutrient status strongly affects the Se biofortification efficiency in rice seedlings by altering the Se subcellular distribution and speciation.

Bidirectional Regulation of Singlet Oxygen Generation from Luminescent Gold Nanoparticles through Surface Manipulation

Singlet oxygen (¹ O₂ ) generation has been observed from ultrasmall luminescent gold nanoparticles (AuNPs), but regulation of ¹ O₂ generation ability from the nanosized noble metals has remained challenging. Herein, the ¹ O₂ generation ability of ultrasmall AuNPs (d ≈ 1.8 nm) is reported to be highly correlated to the surface factors including the amount of Au(I) species and surface charge. By taking the advantages of facile in situ PEGylation, it is discovered that a high amount of Au(I) species and surface charge results in strong ability in generation of ¹ O₂ , whereas a relative low amount of Au(I) species and surface charge leads to weak ability in ¹ O₂ production. A feasible general strategy is then developed to controllably regulate the ¹ O₂ generation efficiency of the AuNPs through facile ligand exchange with positively-charged or negatively-charged thiolated ligands. The AuNPs as nanophotosensitizer for ¹ O₂ generation in the cellular level is also demonstrated to be highly controllable through surface ligand exchange with synergistical effects of ¹ O₂ generation ability and subcellular distribution to lysosome or mitochondria. The strategy in the bidirectional regulation of ¹ O₂ generation from ultrasmall AuNPs provides guidance for future design of nanosized metal nanomedicine toward specific disease diagnosis and treatment.

Influence of Aquatic pH on chemical speciation, phytochelation and vacuolar compartmentalization of arsenic in Vallisneria denseserrulata (Makino)

Arsenic (As) pollution of fresh water has become a major concern worldwide. The present study reports the As accumulation potential and detoxification mechanism in a native plant, Vallisneria denseserrulata (Makino), under different aquatic acidity conditions (pH). V. denseserrulata showed maximum growth at pH ∼7.0 and accumulated ∼1700 mg/kg of As. The increase in pH from 3.5 to 7 significantly (p ≤ 0.05) increased As accumulation, thiol and total protein contents while malondialdehyde (MDA) content, soluble sugar content and percentage electrolytic leakage (%EL) of V. denseserrulata were decreased. The reduction of arsenate [As(V)] to arsenite As(III) was observed as a key step (81% reduction) of the As detoxification in V. denseserrulata. Majority of accumulated As was found in vacuoles (56-72%), while >80% of As in vacuoles was in the form of As(III). FT-IR spectra indicated the complexsation of As with carboxyl, amide, thiol, and hydroxyl groups. Our findings showed the presence of As detoxification mechanism in V. denseserrulata. Vacuolar As compartmentalization and formation of As-Phytochelatins/thiol complexes can be a part of As detoxification mechanisms in V. denseserrulata.

Phytotransformation and Metabolic Pathways of 14C-Carbamazepine in Carrot and Celery

Carbamazepine (CBZ) is an anticonvulsant pharmaceutical compound of environmental concern due to its persistence, bioactive toxicity, and teratogenic effects. Studies on the kinetics and metabolic pathways of CBZ in plant tissues are still limited. In the present study, the phytotransformation of ¹⁴C-CBZ was explored. The ¹⁴C detected in bound residues was lower than in extractable residues (>85% of the uptaken ¹⁴C radioactivity) in plant tissues. CBZ underwent appreciable transformation in plants. A large portion of accumulated ¹⁴C radioactivity (80.3 ± 6.4%) in the cells was distributed in the cell water-soluble fraction. A total of nine radioactive transformation products of CBZ were identified, three of which were generated in vivo due to the contraction of the heterocycle ring. The proposed metabolic pathways revealed that conjugation with glutathione or phenylacetic acid was the major transformation pathway of CBZ in plants, with the contribution of epoxidation, hydroxylation, methoxylation, methylation, amination, and sulfonation.

Biocompatibility studies of fluorescent diamond particles-(NV)~800nm (part V): in vitro kinetics and in vivo localization in rat liver following long-term exposure

Background

We recently reported on long-term comprehensive biocompatibility and biodistribution study of fluorescent nanodiamond particles (NV)-Z-average 800nm (FNDP-(NV)) in rats. FNDP-(NV) primary deposition was found in the liver, yet liver function tests remained normal.

Purpose

The present study aimed to gain preliminary insights on discrete localization of FNDP-(NV) in liver cells of the hepatic lobule unit and venous micro-vasculature. Kinetics of FDNP-(NV) uptake into liver cells surrogates in culture was conducted along with cell cytokinesis as markers of cells' viability.

Methods

Preserved liver specimens from a pilot consisting of two animals which were stained for cytoskeletal elements (fluorescein-isothiocyanate-phalloidin) were examined for distribution of FNDP-(NV) by fluorescent microscopy (FM) and Confocal-FM (CFM) using near infra-red fluorescence (NIR). Hepatocellular carcinoma cells (HepG-2) and human umbilical vein endothelial cells (HUVEC) were cultured with FNDP-(NV) and assayed for particle uptake and location using spectrophotometric technology and microscopy.

Results

HepG-2 and HUVEC displayed rapid (<30 mins) onset and concentration-dependent FNDP-(NV) internalization and formation of peri-nuclear corona. FM/CFM of liver sections revealed FNDP-(NV) presence throughout the hepatic lobules structures marked by spatial distribution, venous microvascular spaces and parenchyma and non-parenchyma cells.

Conclusion

The robust presence of FNDP-(NV) throughout the hepatic lobules including those internalized within parenchyma cells and agglomerates in the liver venous micro-circulation were not associated with macro or micro histopathological signs nor vascular lesions. Cells cultures indicated normal cytokinesis in cells containing FNDP-(NV) agglomerates. Liver parenchyma cells and the liver microcirculation remain agnostic to presence of FNDP-(NV) in the sinusoids or internalized in the hepatic cells.

Guiding Drugs to Target-Harboring Organelles: Stretching Drug-Delivery to a Higher Level of Resolution

The ratio between the dose of drug required for optimal efficacy and the dose that causes toxicity is referred to as the therapeutic window. This ratio can be increased by directing the drug to the diseased tissue or pathogenic cell. For drugs targeting fungi and malignant cells, the therapeutic window can be further improved by increasing the resolution of drug delivery to the specific organelle that harbors the drug's target. Organelle targeting is challenging and is, therefore, an under-exploited strategy. Here we provide an overview of recent advances in control of the subcellular distribution of small molecules with the focus on chemical modifications. Highlighted are recent examples of active and passive organelle-specific targeting by incorporation of organelle-directing molecular determinants or by chemical modifications of the pharmacophore. The outstanding potential that lies in the development of organelle-specific drugs is becoming increasingly apparent.

Cellular Uptake and Distribution of Gemini Surfactant Nanoparticles Used as Gene Delivery Agents

Gemini surfactants are promising molecules utilized as non-viral gene delivery vectors. However, little is known about their cellular uptake and distribution after they release their therapeutic cargo. Therefore, we quantitatively evaluated the cellular uptake and distribution of three gemini surfactants: unsubstituted (16-3-16), with pyridinium head groups (16(Py)-S-2-S-16(Py)) and substituted with a glycyl-lysine di-peptide (16-7N(GK)-16). We also assessed the relationship between cellular uptake and distribution of each gemini surfactant and its overall efficiency and toxicity. Epidermal keratinocytes PAM 212 were treated with gemini surfactant nanoparticles formulated with plasmid DNA and harvested at various time points to collect the enriched nuclear, mitochondrial, plasma membrane, and cytosolic fractions. Gemini surfactants were then extracted from each subcellular fraction and quantified using a validated flow injection analysis-tandem mass spectrometry (FIA-MS/MS) method. Mass spectrometry is superior to the use of fluorescent tags that alter the physicochemical properties and pharmacokinetics of the nanoparticles and can be cleaved from the gemini surfactant molecules within biological systems. Overall, a significantly higher cellular uptake was observed for 16-7N(GK)-16 (17.0%) compared with 16-3-6 (3.6%) and 16(Py)-S-2-S-16(Py) (1.4%), which explained the relatively higher transfection efficiency of 16-7N(GK)-16. Gemini surfactants 16-3-16 and 16(Py)-S-2-S-16(Py) displayed similar subcellular distribution patterns, with major accumulation in the nucleus, followed by the mitochondrion, cytosol, and plasma membrane. In contrast, 16-7N(GK)-16 was relatively evenly distributed across all four subcellular fractions. However, accumulation within the nucleus after 5 h of treatment was the highest for 16(Py)-S-2-S-16(Py) (50.3%), followed by 16-3-16 (41.8%) and then 16-7N(GK)-16 (33.4%), possibly leading to its relatively higher toxicity. Graphical Abstract.

Copper accumulation, subcellular partitioning and physiological and molecular responses in relation to different copper tolerance in apple rootstocks

To unravel the physiological and molecular regulation mechanisms underlying the variation in copper (Cu)accumulation, translocation and tolerance among five apple rootstocks, seedlings were exposed to either basal or excess Cu. Excess Cu suppressed plant biomass and root architecture, which was less pronounced in Malus prunifolia Borkh., indicating its relatively higher Cu tolerance. Among the five apple rootstocks, M. prunifolia exhibited the highest Cu concentration and bio-concentration factor in roots but the lowest translocation factor, indicating its greater ability to immobilize Cu and restrict translocation to the aerial parts. Higher Cu concentration in cell wall fraction but lower Cu proportion in membrane-containing and organelle-rich fractions were found in M. prunifolia. Compared with the other four apple rootstocks under excess Cu conditions, M. prunifolia had a lower increment of hydrogen peroxide in roots and leaves and malondialdehyde in roots, but higher concentrations of carbohydrates and enhanced antioxidants. Transcript levels of genes involved in Cu uptake, transport and detoxification revealed species-specific differences that are probably related to alterations in Cu tolerance. M. prunifolia had relatively higher gene transcript levels including copper transporters 2 (COPT2), COPT6 and zinc/iron-regulated transporter-related protein 2 (ZIP2), which probably took part in Cu uptake, and C-type ATP-binding cassette transporter 2 (ABCC2), copper chaperone for Cu/Zn superoxide dismutase (CCS), Cu/Zn superoxide dismutase 1 (CSD1) and metallothionein 2 (MT2) probably implicated in Cu detoxification, and relatively lower mRNA levels of yellow stripe-like transporter 3 (YSL3) and heavy metal ATPase 5 (HMA5) involved in transport of Cu to aerial parts. These results suggest that M. prunifolia is more tolerant to excess Cu than the other four apple rootstocks under the current experimental conditions, which is probably attributed to more Cu retention in roots, subcellular partitioning, well-coordinated antioxidant defense mechanisms and transcriptional expression of genes involved in Cu uptake, translocation and detoxification.

Subcellular distribution of human tyrosine hydroxylase isoforms 1 and 4 in SH-SY5Y cells

Tyrosine hydroxylase (TH) is the key enzyme that controls the rate of synthesis of the catecholamines. SH-SY5Y cells with stable transfections of either human tyrosine hydroxylase isoform 1 (hTH1) or human tyrosine hydroxylase isoform 4 (hTH4) were used to determined the subcellular distribution of TH protein and phosphorylated TH, under basal conditions and after muscarine stimulation. Muscarine was previously shown to increase the phosphorylation of only serine 19 and serine 40 in hTH1 cells. Under basal conditions, the hTH1 and hTH4 proteins, their serine 19 phosphorylated forms and hTH1 phosphorylated at serine 40 were all similarly distributed; with ~80% in the cytosolic fraction, ~20% in the membrane fraction, and less than 1%, or not detectable, in the nuclear fraction. However, hTH4 phosphorylated at serine 71 had a significantly different distribution with ~65% cytosolic and ~35% membrane associated. Muscarine stimulation led to hTH1 being redistributed from the cytosol and nuclear fractions to the membrane fraction and hTH4 being redistributed from the cytosol to the nuclear fraction. These muscarine stimulated redistributions were not due to TH phosphorylation at serine 19, serine 40, or serine 71 and were most likely due to TH binding to proteins whose phosphorylation was increased by muscarine. This is the first study to show a difference in subcellular distribution between two human TH isoforms under basal and stimulated conditions.

[Differences in the Cadmium-Enrichment Capacity and Subcellular Distribution and Chemical Form of Cadmium in Different Varieties of Pepper]

In a preliminary experiment, 91 pepper varieties were screened, and one variety each with high Cd accumulation (X55), medium Cd accumulation (Daguo 99), and low Cd accumulation (Luojiao 318) were selected to study the effect of different cadmium levels (0, 5, and 10 mg·kg^-1 Cd) on cadmium migration and enrichment ability, and its subcellular distribution and chemical form. The results showed that under the stress of Cd, shoot dry weight of pepper plants was in the order X55>17>27. At the same level of Cd, the Cd transfer coefficient of fruit was 17>27 and X55. Cadmium concentrations in each subcellular component of the pepper fruits were 27 > 17 > X55. Cadmium concentration in subcellular component of the roots, stems, leaves, and fruits of the pepper plants was in order of cell wall (F1) > organelle (F2) > cell soluble component (F3). Cadmium was limited in cell wall and plays an important role in detoxification mechanism and resistance of Cd in pepper plants. The morphological content of various Cd forms in the pepper fruits of the three varieties increased with the increase of Cd treatment level, in the order Cd_NaCl > Cd_HAC > Cd_R > Cd_HCl > Cd_W > Cd_E. Cd_NaCl and Cd_HAC account for a large proportion of Cd in pepper fruits, which may be an important defense mechanism for reducing the biological toxicity of Cd.

Distribution and activation of matrix metalloproteinase-2 in skeletal muscle fibers

A substantial intracellular localization of matrix metalloproteinase 2 (MMP2) has been reported in cardiomyocytes, where it plays a role in the degradation of the contractile apparatus following ischemia-reperfusion injury. Whether MMP2 may have a similar function in skeletal muscle is unknown. This study determined that the absolute amount of MMP2 is similar in rat skeletal and cardiac muscle and human muscle (~10-18 nmol/kg muscle wet wt) but is ~50- to 100-fold less than the amount of calpain-1. We compared mechanically skinned muscle fibers, where the extracellular matrix (ECM) is completely removed, with intact fiber segments and found that ~30% of total MMP2 was associated with the ECM, whereas ~70% was inside the muscle fibers. Concordant with whole muscle fractionation, further separation of skinned fiber segments into cytosolic, membranous, and cytoskeletal and nuclear compartments indicated that ~57% of the intracellular MMP2 was freely diffusible, ~6% was associated with the membrane, and ~37% was bound within the fiber. Under native zymography conditions, only 10% of MMP2 became active upon prolonged (17 h) exposure to 20 μM Ca²⁺, a concentration that would fully activate calpain-1 in seconds to minutes; full activation of MMP2 would require ~1 mM Ca²⁺. Given the prevalence of intracellular MMP2 in skeletal muscle, it is necessary to investigate its function using physiological conditions, including isolation of any potential functional relevance of MMP2 from that of the abundant protease calpain-1.

Uptake, Translocation, and Subcellular Distribution of Azoxystrobin in Wheat Plant ( Triticum aestivum L.)

The uptake mechanism, translocation, and subcellular distribution of azoxystrobin (5 mg kg^-1) in wheat plants was investigated under laboratory conditions. The wheat-water system reached equilibrium after 96 h. Azoxystrobin concentrations in roots were much higher than those in stems and leaves under different exposure times. Azoxystrobin uptake by roots was highly linear at different exposure concentrations, while the bioconcentration factors and translocation factors were independent of the exposed concentration at the equilibrium state. Dead roots adsorbed a larger amount of azoxystrobin than fresh roots, which was measured at different concentrations. Azoxystrobin preferentially accumulated in organelles, and the highest distribution proportion was detected in the soluble cell fractions. This study elucidated that the passive transport and apoplastic pathway dominated the uptake of azoxystrobin by wheat roots. Azoxystrobin primarily accumulated in roots and could be acropetally translocated, but its translocation capacity from roots to stems was limited. Additionally, the uptake and distribution of azoxystrobin by wheat plants could be predicted well by a partition-limited model.

Mitochondrial membrane potential played crucial roles in the accumulation of berberine in HepG2 cells

Berberine is a natural alkaloid that has antineoplastic effects. However, in hepatoma cells like HepG2, the expressions of uptake transporters are minimal but efflux transporters are relatively high. Hence, how berberine enters and reaches a cytocidal concentration remains to be elucidated. In the present study, we revealed the accumulation mechanism of berberine in HepG2 cells. Cell organelles were isolated based on differential centrifugation; berberine concentration was measured using a liquid chromatography-tandem mass chromatography method or flow cytometry. Subcellular distribution of berberine was observed using a laser scanning confocal microscopy. The results showed that berberine was concentration-, temperature-, and time-dependently taken up and accumulated in HepG2 cells. Membrane drug transporters and cell membrane potential had limited effects in berberine uptake. However, qualitative and quantitative studies showed that berberine was enriched in the mitochondria; inhibition of mitochondrial membrane potential (MMP) by carbonyl cyanide 3-chlorophenylhydrazone (CCCP) significantly decreased the intracellular berberine by up to 70%. More importantly, MMP not only significantly enhanced berberine uptake driven by cell membrane potential (P<0.01) but also inhibited p-glycoprotein (P-gp)-mediated berberine efflux (P<0.01). In brief, our results for the first time showed that MMP played crucial roles in berberine accumulation in HepG2 cells.

Circular RNA profiling provides insights into their subcellular distribution and molecular characteristics in HepG2 cells

Circular RNA (circRNA) is a novel RNA molecule that has become a research focus recently. Although some research indicated that the circRNAs in different subcellular compartments could execute different regulatory functions, a panoramic analysis of the subcellular distribution and the transport mechanism of circRNA is still required. In this study, we comprehensively analyzed the subcellular distribution/characteristics and the transport mechanism, through systemically investigating the circRNA profiles among the subcellular fractions of HepG2 cell (nucleus, cytoplasm, mitochondria, ribosome, cytosol and exosome). CircRNAs were widely distributed among the subcellular fractions except in the mitochondria, with differences in the subcellular distribution/characteristics in terms of classification, length, GC content, alternative circularization and parental gene function. Further analysis indicated this might be due to the selective transportation mediated by the transport-related RNA binding proteins (RBPs). The circRNAs may follow the same transportation mechanism of linear RNAs, in which the RBPs specially recognize/transport the RNAs with the corresponding binding motifs. Interestingly, we found that the exosome could selectively package the circRNAs containing the purine-rich 5'-GMWGVWGRAG-3' motif, with the characteristic of 'garbage dumping' and 'intercellular signaling' functions. Besides, although we observed numerous circRNAs enriched in the ribosome, we did not reliably identify any unique-peptides from circRNAs using 3D-LC-MS/MS strategy. This suggests that circRNAs rarely function as translation templates in vivo like lincRNA. Our findings not only indicates the differential distributions/characteristics among the subcellular fractions, but also reveals the possible transportation mechanism. This provides an improved understanding of the life history and molecular behavior of circRNA in cells.

Characteristics of Cd accumulation and distribution in two sweet potato cultivars

In this study, we compared the chemical forms and subcellular distribution of Cd in high-Cd (X16) and low-Cd (N88) sweet potato cultivars through hydroponic experiments and examined the Cd distribution in their roots by histochemical staining. The results showed that inorganic and pectate/protein-integrated Cd predominated in the leaves, and Cd concentrations were significantly higher in X16 than in N88. However, in the roots, Cd was mostly integrated with pectate and protein, and Cd concentration was higher in N88 than in X16. It was mainly stored through vacuolar sequestration and cell wall binding. In the leaves and stems, Cd concentrations in all subcellular fractions were higher in X16 than in N88; the opposite was observed in the roots. In X16, Cd was mostly accumulated in the root stele, and its Cd translocation factor was higher than that of N88. Overall, the subcellular fractions of X16 roots retained less Cd than N88 roots, and more Cd entered the root stele of X16 and subsequently moved to the shoots. The higher amounts of inorganic, water-soluble, and pectate/protein-integrated Cd with high mobility in the shoots of X16 than in N88 might facilitate Cd remobilization to other tissues, but this needs to be further studied.

Subcellular distribution, chemical forms, and physiological response to cadmium stress in Hydrilla verticillata

This study investigated the subcellular distribution and chemical forms of cadmium (Cd) in Hydrilla verticillata and the physiological mechanism underlying H. verticillata responses to Cd stress. Hydrilla verticillata was grown in a hydroponic system and was treated with various Cd concentrations (0, 10, 50, 100, 125, and 150 µM) for 7 days. Cadmium analysis of the leaves at the subcellular level showed that Cd was mainly stored in the soluble fraction (77.98-83.62%) and in smaller quantities in the cell wall fraction (11.99-17.30%) and the cell organelles (4.30-4.88%). The Cd taken up by H. verticillata was in different chemical forms. In the leaves and stems, the Cd was mostly extracted using 1 M NaCl and smaller amounts of Cd were extracted using 2% acetic acid. The malondialdehyde content significantly increased at all Cd concentrations, which indicated oxidative stress. The superoxide dismutase, guaiacol peroxidase, and catalase activities were enhanced. The proline, ascorbate, and glutathione contents increased at lower Cd concentrations, but decreased consistently as the Cd concentration rose. These results suggest that H. verticillata can be successfully used in the phytoremediation of Cd-contaminated water.

Subcellular cadmium distribution and antioxidant enzymatic activities in the leaves of four Hylotelephium spectabile populations exhibit differences in phytoextraction potential

Hylotelephium spectabile with high tolerance to cadmium (Cd) might be a potential candidate for phytoremediation. However, the mechanisms for Cd accumulation and tolerance in H. spectabile are poorly understood. Four H. spectabile populations, namely HB1, HB2, JS, and LN, were selected to investigate their Cd extraction potential and the underlying mechanism of Cd accumulation, focusing on subcellular distribution and antioxidant enzymes. The Cd concentration, bioconcentration factor and transfer factor of the LN was significantly higher than other populations, particularly with increasing Cd exposure, and no obvious growth inhibition observed. Segregation of excessive Cd to Cd-rich granule in LN was much higher than other populations which reveal one possible mechanism of Cd accumulation. A significant increase in superoxide dismutase (SOD) and catalase (CAT) activities with increasing Cd stress suggested SOD and CAT contribute to the Cd tolerance of H. spectabile. LN displayed significantly higher and constant peroxidase (POD) activities than other populations, which indicated that an effective mechanism existed in the LN to cope with Cd stress. Therefore, the subcellular distribution and antioxidant enzymes might play important roles in Cd accumulation and tolerance of H. spectabile. LN possessed high Cd extraction potential, and further studies under field conditions are warranted.

Exogenous spermidine elevating cadmium tolerance in Salix matsudana involves cadmium detoxification and antioxidant defense

In this study, exogenous spermidine role on Salix matsudana tolerance to cadmium was evaluated. Spermidine and cadmium presented antagonistic effects on the biomass, copper and zinc concentrations in S. matsudana. cadmium mainly distributed in the cell wall of subcellular fraction; 46.97%-60.43% of cadmium existed in a sodium chloride-extracted form. Cadmium contents in roots, leaves, and twigs ranged from 2002.67 to 3961.00, 111.59 to 229.72, and 102.56 to 221.27 mg/kg, respectively. Spermidine application elevated cadmium concentrations in the roots, cuttings, and cell wall and the ratio of deionized water-extracted cadmium, but decreased cadmium levels in the twigs and leaves and the fractions of cadmium extracted by ethanol and sodium chloride, respectively. Putrescine and malondialdehyde were important indicators of cadmium-induced oxidative damage. Exogenous spermidine alleviated the accumulation of superoxide anion, hydrogen peroxide, malondialdehyde via promoting the levels of spermidine, soluble protein, superoxide dismutase, reductive ascorbate, glutathione reductase, and glutathione peroxidase in S. matsudana leaves under the corresponding cadmium stress. The results indicated that S. matsudana was a candidate for cadmium rhizoremediation and extraction in leaves; the spermidine application enhanced the cadmium tolerance of S. matsudana through promoting cadmium accumulation in roots, cell wall, and less bioactive chemical forms and the antioxidative ability.

Transporter-Mediated Subcellular Distribution in the Metabolism and Signaling of Jasmonates

Jasmonates (jasmonic acid and its relatives) are a group of oxylipin phytohormones that are implicated in the regulation of a range of developmental processes and responses to environmental stimuli in plants. The biosynthesis of JAs occur sequentially in various subcellular compartments including the chloroplasts, peroxisomes and the cytoplasm. The biologically active jasmonoyl-isoleucine (JA-Ile) activates the core JA signaling in the nucleus by binding with its coreceptor, SCF^COI1-JAZ. Five members of a clade of ATP-binding cassette G (ABCG) transporters of Arabidopsis thaliana were identified as the candidates of jasmonate transporters (JATs) in yeast cells. Among these JATs, AtJAT1/AtABCG16, has a dual localization in the plasma membrane and nuclear envelop and mediates the efflux of jasmonic acid (JA) across the plasma membrane and influx of JA-Ile into the nucleus. Genetic, cellular and biochemical analyses have demonstrated that AtJAT1/AtABCG16 is crucial for modulating JA-Ile concentration in the nucleus to orchestrate JA signaling. AtJAT1 could also be involved in modulating the biosynthesis of JA-Ile by regulating the distribution of JA and JA-Ile in the cytoplasm and nucleus, which would contribute to the highly dynamic JA signaling. Furthermore, other JAT members are localized in the plasma membrane and possibly in peroxisomes. Characterization of these JATs will provide further insights into a crucial role of transporter-mediated subcellular distribution in the metabolism and signaling of plant hormones, an emerging theme supported by the identification of increasing number of endomembrane-localized transporters.